In electronic devices, e.g., notebook personal computers, the amount of heat generated from internal components has increased in accordance with improvements in the performance of the devices. In the case where such an electronic device is used, when the outside air temperature is high or the condition of the installation location of the device is bad, the heat is not dissipated sufficiently and the operation of the device may become unstable. Japanese Unexamined Patent Application Publication No. 2004-179271 (PTL 1) discloses a cooling mat, in which an endothermic agent is encapsulated in a flat bag of resin film, aluminum foil, or the like, for the purpose of cooling such an electronic device. The operation of the electronic device, e.g., a personal computer, can be stabilized by laying this cooling mat under the electronic device. Also, Japanese Unexamined Patent Application Publication No. 2002-138205 (PTL 2) describes a single-plate-like, flexible, thermally conductive sheet used for heat dissipation.